Laser ordnance initiators use a laser to initiate an explosive via an optical fiber. Such initiators are reliable and generally make unintentional initiation difficult. Safety features for such laser ordnance initiators are governed by the United States Department of Defense military standard MIL-STD-1901A titled “Design Criteria Standard for Munition Rocket and Missile Motor Ignition System Design”. The standard requires all such designs to include an ignition safety device (ISD), or SAFE-ARM device, whose purpose is to prevent an unintended function of the rocket or missile motor through interruption of the pyrotechnic train, interruption of the firing energy train, or control of the energy required to arm the ISD and operate the initiator. More specifically, the standard requires low-power ignition systems to employ a SAFE-ARM device that provides a physical interruption in the laser energy path between a laser firing unit (or source) and the intended target ordnance (or receptor) to prevent inadvertent ordnance operation.
Paragraph 5.2.3.1 of MIL-STD-1901A provides compliance criteria for firing energy train interruption with low voltage devices and provides an example of a firing energy train, which would require interruption, is an ignition system using a low voltage (activated by less than 500 volts) laser diode, with associated optical transmission hardware and an approved in line pyrotechnic. At least one firing energy train interrupter is required if low voltage devices are used. Low voltage devices are defined as those incorporating initiators requiring less than 500 volts or less than the maximum voltage available in the ignition system prior to commit to launch (whichever is greater). Interruption of the low voltage alone in these applications is not an acceptable design. The design of the firing energy train interruption shall comply with the following:    a. The interrupter shall be rendered ineffective by the arming energy and automatically return to a non-armed state upon removal of the arming energy.    b. If the first pyrotechnic element is positioned such that safety is dependent upon the presence of an interrupter, the design shall include positive means to prevent the ISD from being assembled without the properly positioned interrupter.    c. If the first pyrotechnic element is positioned such that omission of the interrupter will prohibit transfer to the pyrotechnic train, a single interrupter is acceptable.    d. The effectiveness of the interruption prior to initiation of the arming sequence shall be determined numerically and the methodology and results presented and justified to the appropriate service safety authority.
The conventional approach for providing SAFE-ARM functionality to laser initiated ordnance systems (LIOS) has been to relegate the function to electronic circuitry and to not provide a physical interruption or ‘block’ in the laser optical ignition train. As such, there is a need for an improved SAFE-ARM and distribution device for a LIOS that complies with MIL-STD-1901A.